Bdtjtk

I have the following code:

              real          :: s_s, d_s, s_r(size), d_r(size)

              integer       :: k, k_r(size)



              ! - size = number of processors

              ! - Do something to initialise s_s, d_s, k

              write(*,*) "SENDING >>>>"

              write(*,*) s_s, d_s

              call MPI_Allgather( s_s, 1, MPI_REAL,

 &                 s_r, 1, MPI_REAL, MPI_COMM_PGM, mpi_err)



              call MPI_Allgather( d_s, 1, MPI_REAL,

 &                 d_r, 1, MPI_REAL, MPI_COMM_PGM, mpi_err)



              call MPI_Allgather ( k, 1, MPI_INTEGER,

 &                 k_r, 1, MPI_INTEGER, MPI_COMM_PGM, mpi_err)





              write(*,*) "RECEIVED <<<<"

              write(*,*) s_r, d_r, kr

This generates the following output:

SENDING >>>>

  -1803.80339864908       0.616157856320407     

 RECEIVED <<<<

  6.953077622513053E-310  3.565412685916647E-314  1.221334434576037E-314

  1.498827614035474E-314  6.952991536467244E-310  6.953288052096687E-310

  6.953108563966064E-310  2.350861403096908E-314           4           1

           2           3

kr is being gathered correctly however, s_r and d_r seem to be receiving junk. Could this be because of the MPI datatypes? I tried with MPI_REAL MPI_REAL8 and MPI_DOUBLE but that didn't work. Furthermore, mpi_err = MPI_SUCCESS

What could I do to resolve this?

EDIT 1
I worked on the following prototype program:

program allgather

  implicit none



  include "mpif.h"



  real a(4)

  integer rank,size,ierr

  real as(4)

  real ar(16)

  integer i, j, k,z 



  a=1

  call MPI_INIT(ierr)

  call MPI_COMM_RANK(MPI_COMM_WORLD, rank, ierr)

  call MPI_COMM_SIZE(MPI_COMM_WORLD, size, ierr)

  if(size.ne.4)then 

     write(*,*)'Error!:# of processors must be equal to 4'

     write(*,*)'Programm aborting....'

     call MPI_ABORT(ierr)

  endif



  do k=1,4

     if ( rank == (mod(k, size))) then

        a(k)  = k

     else

        a(k)  = 0.0 

     endif

  enddo



  write(*,*) "Rank :", rank

  write(*,*) a



  call MPI_Allgather(a, 4, MPI_REAL, ar,

 &     4,

 &     MPI_REAL, MPI_COMM_WORLD, ierr)



  write(*,*) "Recieved array"

  write(*,*) ar



  do i = 1, 16

     if ( ar(i) /= 0.0 ) then

        z = mod(i, size)

        if ( z == 0 ) then

           a( size ) = ar(i)

        else

           a ( z ) = ar(i)

        endif

     endif

  enddo



  write(*,*) "---------"

  write(*,*) a

  write(*,*) "---------"



  call MPI_FINALIZE(ierr)

  end

And this generates the expected results i.e. ar doesn't gather junk. I'm unable to however tell the difference between the implementations.

It turns out that for the project, the data type to be used was MPI_FLT. It is strange that MPI_FLT works and not MPI_REALx where x=4,8 also not MPI_FLOAT. I grep-ed MPI_FLT in the project to see what it is defined as but didn't turn up anywhere in the project.

The OpenMPI version I'm using is:

$ mpirun --version

mpirun (Open MPI) 3.0.0

The compiler I use is:

$ mpifort --version

ifort (IFORT) 19.0.1.144 20181018

In a future edit I will elaborate on the cause.